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Electrochemical water splitting is a viable strategy to produce renewable fuels such as hydrogen. Oxygen evolution reaction (OER) at the anode is getting more attention than hydrogen evolution reaction (HER) because of its higher overpotential and slower electron transfer process. Many advancements in the construction of an effective electrocatalyst have been made recently in an effort to boost OER activity. Additionally, the commercial RuO2 and Pt-derived catalysts are the most fascinating and active electrocatalysts used in the OER and HER kinetics procedure. They show good activity but the massive price and insufficiency are the main obstacles to their widespread usage in the production of hydrogen and oxygen gas. In this case, SnS2_multi walled carbon nanotubes (MWCNTSs) are directly produced on nickel foam (NF) using hydrothermal synthesis. All the catalysts like SnS2, MWCNTSs, and SnS2_MWCNTSs have been developed, and then they are characterized for structural, morphological, compositional, and electrochemical characterization. The fabricated nanocomposite shows OER onset potential of 1.33 V, 116 mV overpotential at 10 mAcm−2, and has a Tafel slope of 47 mVdec−1. In contrast, its HER onset potential is −0.3 V having 209 mV overpotential at 10 mAcm−2 current density and a Tafel slope of 135 mVdec−1. The presence of more electroactive sites, the lowest charge transfer resistance at the electrode-electrolyte interface, the distinct and uniform nanocrystal-like morphology, and the synergistic interaction between SnS2 and MWCNTS are some of the factors that contribute to the low value of overpotential of SnS2_MWCNTSs. The resultant electrocatalyst worked well for the very effective oxidation of water and has a variety of possible applications. Highlights: The SnS2_multi walled carbon nanotube (MWCNT) are directly grown on nickel foam (NF) using hydrothermal method. The SnS2_MWCNT are characterized for structural, morphological, compositional, and electrochemical characterization using various analytical tools. The SnS2_MWCNT shows OER overpotential of 116 mV at 10 mAcm−2 and has a Tafel slope of 47 mVdec−1. The SnS2_MWCNT shows HER overpotential 209 mV at 10 mAcm−2 and a Tafel slope of 135 mVdec−1. [ABSTRACT FROM AUTHOR]

Most electrocatalysts are known to experience structural change during the oxygen evolution reaction (OER) process. Considerable endeavors have been dedicated thus far to comprehending the catalytic process and uncovering the underlying mechanism. During the dynamic evolution of catalyst structure, component leaching of electrocatalysts is the most common phenomenon. This article offers a concise overview of recent findings and developments related to the leaching phenomena in the OER process in terms of fundamental understanding of leaching, advanced characterization techniques used to investigate leaching, leaching of inactive components, and leaching of active components. Leaching behaviors and the induced effects in various kinds of OER catalysts are discussed, progress in manipulating leaching amount/degree toward a tunable surface evolution is spotlighted, and finally, three representative types of structure transformations induced by leaching metastable species in OER condition are proposed. By understanding the process of component leaching in the OER, it will provide more guidance for the rational design of superior electrocatalysts. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting is regarded as a potential technique for converting solar energy. However, the fast charge recombination and slow water oxidation kinetics significantly have hindered its practical application. It is found that an elevation in operation temperature can activate the charge transport in the photoanodes. Here, a strategy was performed that carbon nanoparticles were employed to TiO2 nanorods, acting as electron reservoirs as well as photothermal materials. More specifically, a record photocurrent density of 1.62 mA cm−2 at 1.23 V vs. RHE has been achieved, accompanied by a high charge separation efficiency of 96% and a long-term durability for 8 h. The detailed experimental results reveal that under NIR light irradiation, the synergistic effect between electron storage and temperature rise leads to accelerated charge transport in the bulk and water oxidation kinetics on the surface. This research offers a new perspective on how to boost the PEC performance of photoelectrodes. [ABSTRACT FROM AUTHOR]

One of the reasons for the high efficiency and selectivity of biological catalysts arise from their ability to control the pathways of substrates and products using protein channels, and by modulating the transport in the channels using the interaction with the protein residues and the water/hydrogen-bonding network. This process is clearly demonstrated in Photosystem II (PS II), where its light-driven water oxidation reaction catalyzed by the Mn4CaO5 cluster occurs deep inside the protein complex and thus requires the transport of two water molecules to and four protons from the metal center to the bulk water. Based on the recent advances in structural studies of PS II from X-ray crystallography and cryo-electron microscopy, in this review we compare the channels that have been proposed to facilitate this mass transport in cyanobacteria, red and green algae, diatoms, and higher plants. The three major channels (O1, O4, and Cl1 channels) are present in all species investigated; however, some differences exist in the reported structures that arise from the different composition and arrangement of membrane extrinsic subunits between the species. Among the three channels, the Cl1 channel, including the proton gate, is the most conserved among all photosynthetic species. We also found at least one branch for the O1 channel in all organisms, extending all the way from Ca/O1 via the 'water wheel' to the lumen. However, the extending path after the water wheel varies between most species. The O4 channel is, like the Cl1 channel, highly conserved among all species while having different orientations at the end of the path near the bulk. The comparison suggests that the previously proposed functionality of the channels in T. vestitus (Ibrahim et al., Proc Natl Acad Sci USA 117:12624-12635, 2020; Hussein et al., Nat Commun 12:6531, 2021) is conserved through the species, i.e. the O1-like channel is used for substrate water intake, and the tighter Cl1 and O4 channels for proton release. The comparison does not eliminate the potential role of O4 channel as a water intake channel. However, the highly ordered hydrogen-bonded water wire connected to the Mn4CaO5 cluster via the O4 may strongly suggest that it functions in proton release, especially during the S0 → S1 transition (Saito et al., Nat Commun 6:8488, 2015; Kern et al., Nature 563:421-425, 2018; Ibrahim et al., Proc Natl Acad Sci USA 117:12624-12635, 2020; Sakashita et al., Phys Chem Chem Phys 22:15831-15841, 2020; Hussein et al., Nat Commun 12:6531, 2021).

Recently, tungsten oxide (WO 3) and bismuth vanadate (BiVO 4) have been considered as an intriguing combination for constructing a heterojunction for efficient photoelectrochemical (PEC) applications. Herein, we report the preparation of ternary WO 3 /BiVO 4 /NiCo layered double hydroxide (LDH) photoanodes for boosting photogenerated carrier transport and promotion of catalytic activity. WO 3 /BiVO 4 heterostructures were synthesized by a hydrothermal process of WO 3 nanoplates on a fluorine-doped tin oxide (FTO) glass substrate, followed by spin-coating for BiVO 4 materials. We investigated the effect of a NiCo LDH catalyst on PEC performance by controlling the growth temperatures of the NiCo LDH via hydrothermal synthesis. Moreover, the X-ray diffraction (XRD), Fourier‒transform infrared (FTIR) and X‒ray photoelectron spectroscopy (XPS) analyses revealed that the WO 3 /BiVO 4 heterojunction was retained after the NiCo LDH growth process regardless of synthesis temperatures. The PEC results verified that the WO 3 /BiVO 4 heterostructure with the optimized NiCo LDH catalyst (WBN60) possessed the best photocurrent density of 3.2 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE), which created improved charge separation and surface oxidation kinetics of photogenerated carriers. Consequentially, the smallest charge transfer resistance and recombination rate were achieved in the WBN60 electrode compared to others, indicating a much lower photoelectrode‒electrolyte interfacial resistance and the enhancement of photogenerated carrier transport by suppressing recombination. [ABSTRACT FROM AUTHOR]

Protein structure plays an essential role on their stability, functionality, and catalytic activity. In this work, the interplay between the β‐sheet structure and its catalytic implications to the design of enzyme‐inspired materials is investigated. Here, inspiration is drawn from the active sites and β‐sheet rich structure of the highly efficient multicopper oxidase (MCO) to engineer a bio‐inspired electrocatalyst for water oxidation utilizing the abundant metal, copper. Copper ions are coordinated to poly‐histidine (polyCuHis), as they are in MCO active sites. The resultant polyCuHis material effectively promotes water oxidation with low overpotentials (0.15 V) in alkaline systems. This activity is due to the 3D structure of the poly‐histidine backbone. By increasing the prevalence of β‐sheet structure and decreasing the random coil nature of the polyCuHis secondary structures, this study is able to modulates the electrocatalytic activity of this material is modulated, shifting it toward water oxidation. These results highlight the crucial role of the local environment at catalytic sites for efficient, energy‐relevant transformations. Moreover, this work highlights the importance of conformational structure in the design of scaffolds for high‐performance electrocatalysts. [ABSTRACT FROM AUTHOR]

X-ray crystallography and X-ray spectroscopy using X-ray free electron lasers plays an important role in understanding the interplay of structural changes in the protein and the chemical changes at the metal active site of metalloenzymes through their catalytic cycles. As a part of such an effort, we report here our recent development of methods for X-ray absorption spectroscopy (XAS) at XFELs to study dilute biological samples, available in limited volumes. Our prime target is Photosystem II (PS II), a multi subunit membrane protein complex, that catalyzes the light-driven water oxidation reaction at the Mn4CaO5 cluster. This is an ideal system to investigate how to control multi-electron/proton chemistry, using the flexibility of metal redox states, in coordination with the protein and the water network. We describe the method that we have developed to collect XAS data using PS II samples with a Mn concentration of

Abstract Most electrocatalysts are known to experience structural change during the oxygen evolution reaction (OER) process. Considerable endeavors have been dedicated thus far to comprehending the catalytic process and uncovering the underlying mechanism. During the dynamic evolution of catalyst structure, component leaching of electrocatalysts is the most common phenomenon. This article offers a concise overview of recent findings and developments related to the leaching phenomena in the OER process in terms of fundamental understanding of leaching, advanced characterization techniques used to investigate leaching, leaching of inactive components, and leaching of active components. Leaching behaviors and the induced effects in various kinds of OER catalysts are discussed, progress in manipulating leaching amount/degree toward a tunable surface evolution is spotlighted, and finally, three representative types of structure transformations induced by leaching metastable species in OER condition are proposed. By understanding the process of component leaching in the OER, it will provide more guidance for the rational design of superior electrocatalysts.

The oxygen evolution reaction (OER) is a vital half-reaction in many applications, such as the electrochemical H2O splitting, CO2, and N2 conversion processes. The OER involves a four-electron transfer and is a kinetically sluggish reaction that requires additional potential to drive. To enhance the electrochemical performance of the above-mentioned applications, highly efficient, corrosion-resistant, earth-abundant, and eco-friendly electrocatalysts are required. Here, we report a highly porous, minimally Ru-doped copper phosphate electrocatalyst obtained through co-precipitation. The optimized electrocatalyst (5% Ru-doped copper phosphate) exhibits a low overpotential of 340 mV to achieve 10 mA cm−2 compared to copper-based materials, and it remains stable over 20 h. The high performance is attributed to a high electrochemically effective surface area (ECSA) of 30.25 cm2, facilitating effective ion transportation at the electrode/electrolyte interface and excellent electrical conductivity. This result is supported by density functional theory calculations, which demonstrate that ruthenium enhances the electrochemical properties by increasing electronic conductivity, reducing the theoretical overpotential, and influencing the rate-determining step of the oxygen evolution reaction. Herein, the electrocatalyst is attractive for commercialization due to its utilization of minimal ruthenium in earth-abundant electrocatalysts, which offer competitive performance.

Photoelectrochemical (PEC) water splitting is regarded as a potential technique for converting solar energy. However, the fast charge recombination and slow water oxidation kinetics significantly have hindered its practical application. It is found that an elevation in operation temperature can activate the charge transport in the photoanodes. Here, a strategy was performed that carbon nanoparticles were employed to TiO2 nanorods, acting as electron reservoirs as well as photothermal materials. More specifically, a record photocurrent density of 1.62 mA cm−2 at 1.23 V vs. RHE has been achieved, accompanied by a high charge separation efficiency of 96% and a long-term durability for 8 h. The detailed experimental results reveal that under NIR light irradiation, the synergistic effect between electron storage and temperature rise leads to accelerated charge transport in the bulk and water oxidation kinetics on the surface. This research offers a new perspective on how to boost the PEC performance of photoelectrodes.

Abstract Protein structure plays an essential role on their stability, functionality, and catalytic activity. In this work, the interplay between the β‐sheet structure and its catalytic implications to the design of enzyme‐inspired materials is investigated. Here, inspiration is drawn from the active sites and β‐sheet rich structure of the highly efficient multicopper oxidase (MCO) to engineer a bio‐inspired electrocatalyst for water oxidation utilizing the abundant metal, copper. Copper ions are coordinated to poly‐histidine (polyCuHis), as they are in MCO active sites. The resultant polyCuHis material effectively promotes water oxidation with low overpotentials (0.15 V) in alkaline systems. This activity is due to the 3D structure of the poly‐histidine backbone. By increasing the prevalence of β‐sheet structure and decreasing the random coil nature of the polyCuHis secondary structures, this study is able to modulates the electrocatalytic activity of this material is modulated, shifting it toward water oxidation. These results highlight the crucial role of the local environment at catalytic sites for efficient, energy‐relevant transformations. Moreover, this work highlights the importance of conformational structure in the design of scaffolds for high‐performance electrocatalysts.

[Display omitted] Molybdenum carbide materials with unique electronic structures have received special attention as water-splitting catalysts, but their structural stability in the alkaline water electrolysis process is not satisfactory. This study reports an in situ pyrolysis method for preparing NiMo-based metal-organic framework (MOF)-derived chain-mail oxygen evolution reaction (OER) electrocatalysts and bamboo-like N-doped carbon nanotube (NCNT)-encapsulated Ni-doped MoC nanoparticles (NiMoC-NCNTs). The NCNTs can provide chain mail shells to protect the inner highly reactive Ni-doped MoC cores from electrochemical corrosion by the alkaline electrolyte and regulate their catalytic properties through charge redistribution. Benefiting from high N -doping with abundant pyridinic moieties and abundant active sites of the periodic bamboo-like nodes, the as-prepared NiMoC-NCNTs display an outstanding activity for the OER with an overpotential of 310 mV at 10 mA cm−2 and a superior long-term stability of 50 h. Density functional theory calculations reveal that the excellent electrocatalytic activity of NiMoC-NCNTs comes from the electron transfer from NiMoC nanoparticles to NCNTs, resulting in a decrease in the local work function at the carbon surface and optimized free efficiencies of OER intermediates on C sites. This work provides an effective approach to improve the structural stability of fragile catalysts by equipping them with carbon-based chain. [ABSTRACT FROM AUTHOR]

Mn-oxidizing microorganisms oxidize environmental Mn(II), producing Mn(IV) oxides. Pseudomonas putida MnB1 is a widely studied organism for the oxidation of manganese(II) to manganese(IV) by a multi-copper oxidase. The biogenic manganese oxides (BMOs) produced by MnB1 and similar organisms have unique properties compared to non-biological manganese oxides. Along with an amorphous, poorly crystalline structure, previous studies have indicated that BMOs have high surface areas and high reactivities. It is also known that abiotic Mn oxides promote oxidation of organics and have been studied for their water oxidation catalytic function. MnB1 was grown and maintained and subsequently transferred to culturing media containing manganese(II) salts to observe the oxidation of manganese(II) to manganese(IV). The structures and compositions of these manganese(IV) oxides were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma optical emission spectroscopy, and powder X-ray diffraction, and their properties were assessed regarding catalytic functionality towards water oxidation in comparison to abiotic acid birnessite. Water oxidation was accomplished through the whole-cell catalysis of MnB1, the results for which compare favorably to the water-oxidizing ability of abiotic Mn(IV) oxides. [ABSTRACT FROM AUTHOR]

Mimicking the photosynthesis of green plants to combine water oxidation with CO2 reduction is of great significance for solving energy and environmental crises. In this context, a trinuclear nickel complex, [NiII3(paoH)6(PhPO3)2]·2ClO4 (1), with a novel structure has been constructed with PhPO32− (phenylphosphonate) and paoH (2-pyridine formaldehyde oxime) ligands and possesses a reflection symmetry with a mirror plane revealed by single-crystal X-ray diffraction. Bulk electrocatalysis demonstrates that complex 1 can homogeneously catalyze water oxidation and CO2 reduction simultaneously. It can catalyze water oxidation at a near-neutral condition of pH = 7.45 with a high TOF of 12.2 s−1, and the Faraday efficiency is as high as 95%. Meanwhile, it also exhibits high electrocatalytic activity for CO2 reduction towards CO with a TOF of 7.84 s−1 in DMF solution. The excellent electrocatalytic performance of the water oxidation and CO2 reduction of complex 1 could be attributed to the two unique µ3-PhPO32− bridges as the crucial factor for stabilizing the trinuclear molecule as well as the proton transformation during the catalytic process, while the oxime groups modulate the electronic structure of the metal centers via π back-bonding. Therefore, apart from the cooperation effect of the three Ni centers for catalysis, simultaneously, the two kinds of ligands in complex 1 can also synergistically coordinate the central metal, thereby significantly promoting its catalytic performance. Complex 1 represents the first nickel molecular electrocatalyst for both water oxidation and CO2 reduction. The findings in this work open an avenue for designing efficient molecular electrocatalysts with peculiar ligands. [ABSTRACT FROM AUTHOR]

The progression of technology has been continuing for last centuries and it accelerated in the twenty first century. Nanoscience and nanotechnology help to discover an enormous number of economical and sustainable materials. The most economical and sustainable materials, two-dimensional (2D) materials have blessed a good platform to explore them in nano- and atomic-level applications. The discovery of graphene has encouraged considerable intentness to scientists to investigate other novel 2D materials, which is modern-day "alchemy". In designing material for a specific feature, it's important to consider the physical dimensions in addition to chemical capabilities. The photo-chemical capabilities of materials can be influenced by their physical dimension, optical properties, surface area, and mechanical properties. The surface area for executing the photoelectric effect and the long-range conductivity for homogeneous charge distribution in carrying out the photochemical reactions are perfectly balanced in 2D materials. To date, a wide range of 2D materials have been investigated, all of which are low-cost, stable, earth-abundant, and free of hazards. However, the efficiency of photocatalysts must be improved to meet the growing prerequisite for green energy in modernizing society. Photocatalysts are particularly interested in storing solar energy in chemical bonds to supply sustainable energy. This review will provide the very recent contributions on modifying 2D materials to connect the collective effort in developing photocatalysts for water oxidation. Also, different physical and chemical methods for the preparation of catalysts are included with their advantages and drawback. Furthermore, we will emphasize the perspective, challenges, and dimensions of the ongoing work in the conclusion part. [ABSTRACT FROM AUTHOR]

Water oxidation is one of the most important reactions needed for a transition to a green economy. The reaction relies on extracting electrons from oxygen anions and is commonly studied using homogenous catalysts based on Ru or Ir metals. Because of Ir scarcity and its relative instability in acidic environments, metals to replace it are sought after. In this study, we have synthesized Au-Pd-based catalysts deposited on TiO2 with different ratios in order to mimic IrO2 valence orbitals (Ir5d) by the hybrid valence orbitals of Au5d and Pd4d and compared their heterogeneous catalytic activity for the evolution of O2 from water in the presence of cerium ammonium nitrate (CAN). Au-Pd-based catalysts were found to be active at a particular nominal atomic ratio. At an atomic ratio of 1 Au to 2 Pd and 1 Au to 3 Pd, the catalysts were active and stable for oxygen production from water. Long-term runs up to 20,000 min still showed the expected stoichiometry between O2 production and CAN consumption (1 to 4). However, catalysts with a reverse ratio were not active. Also, the monometallic catalysts were found to be not active for the reaction. We link the reason for the activity of Au-Pd with this specific ratio to the shape and energy position of their valence band that might be similar to those of IrO2 particles. While the turnover numbers of the Au-Pd-based catalysts were found to be lower than those of IrO2-based catalysts, on the same support in a heterogenous system, there is considerable potential upon further optimization for these two metals to replace IrO2 for a water oxidation reaction. [ABSTRACT FROM AUTHOR]

Water oxidation is a multielectron complex reaction that produces molecular oxygen as the final product. The article addresses the lack of confirmation of oxygen product formation in electrochemical oxygen evolution reaction (OER) studies, despite the extensive research conducted on catalysts for water splitting. It critically evaluates the trend observed in many studies that solely rely on electrochemical methods for OER quantification without confirming the oxygen product via complementary analytical techniques. The omission of measuring evolved oxygen gas leaves a crucial gap in the quantification of the OER process and raises concerns about the validity and accuracy of reported results. Analytical techniques, such as gas chromatography, Rotating Ring-Disk Electrode (RRDE), fluorescence oxygen probes, Clark electrode, and volumetry are critically analyzed and described to ensure the reliability and credibility of voltammetry and bulk electrolysis to provide a more accurate assessment of the OER process. [ABSTRACT FROM AUTHOR]

Abstract BiVO4 is one of the most promising photoanode materials for photoelectrochemical (PEC) solar energy conversion, but it still suffers from poor photocurrent density due to insufficient light‐harvesting efficiency (LHE), weak photogenerated charge separation efficiency (ΦSep), and low water oxidation efficiency (ΦOX). Herein, we tackle these challenges of the BiVO4 photoanodes using systematic engineering, including catalysis engineering, bandgap engineering, and morphology engineering. In particular, we deposit a NiCoOx layer onto the BiVO4 photoanode as the oxygen evolution catalyst to enhance the ΦOX of Fe‐g‐C3N4/BiVO4 for PEC water oxidation, and incorporate Fe‐doped graphite‐phase C3N4 (Fe‐g‐C3N4) into the BiVO4 photoanode to optimize the bandgap and surface areas to subsequently expand the light absorption range of the photoanode from 530 to 690 nm, increase the LHE and ΦSep, and further improve the oxygen evolution reaction activity of the NiCoOx catalytic layer. Consequently, the maximum photocurrent density of the as‐prepared NiCoOx/Fe‐g‐C3N4/BiVO4 is remarkably boosted from 4.6 to 7.4 mA cm−2. This work suggests that the proposed systematic engineering strategy is exceptionally promising for improving LHE, ΦSep, and ΦOX of BiVO4‐based photoanodes, which will substantially benefit the design, preparation, and large‐scale application of next‐generation high‐performance photoanodes.

Photosystem II (PSII) enables global-scale, light-driven water oxidation. Genetic manipulation of PSII from the mesophilic cyanobacterium Synechocystis sp. PCC 6803 has provided insights into the mechanism of water oxidation; however, the lack of a high-resolution structure of oxygen-evolving PSII from this organism has limited the interpretation of biophysical data to models based on structures of thermophilic cyanobacterial PSII. Here, we report the cryo-electron microscopy structure of PSII from Synechocystis sp. PCC 6803 at 1.93-Å resolution. A number of differences are observed relative to thermophilic PSII structures, including the following: the extrinsic subunit PsbQ is maintained, the C terminus of the D1 subunit is flexible, some waters near the active site are partially occupied, and differences in the PsbV subunit block the Large (O1) water channel. These features strongly influence the structural picture of PSII, especially as it pertains to the mechanism of water oxidation.

How to put together a comprehensive water oxidation design is the long‐term problem for the generation of sustainable fuels. In nature, plants are equipped with a complex mechanism (the Calvin cycle) in the stroma that, over the billions of years, efficiently takes CO2 and converts it to sugar. This reductive process needs electrons from an oxygen‐evolving complex (OEC) in the core of photosystem II, where a water oxidation reaction (WOR) releases molecular oxygen. The initial function of proton relays in natural WOR happens when Tyrosine Yz is oxidized by light harvested P680 through a proton‐coupled electron transfer reaction. The second and main one, is composed of water‐included polypeptide channels from and to CaMn4O5. These channels were created utilizing hydrogen‐bonded networks (HBN). HBN is crucial in providing water substrate and removing the released protons to prevent the accumulation of protons and preserve the stability of the catalytic center. This concept summarizes the challenges in employing biomimicry to create artificial leaves from the viewpoint of proton relays, with the main purpose being providing structural functionality to assist the quick proton hopping. [ABSTRACT FROM AUTHOR]

Emerging as a new class of advanced functional materials with hierarchical architectures and redox characters, organic–inorganic hybrid materials (OIHs) have been well developed and widely applied in various energy conversion reactions recently. In this review, we focus on the applications and structure–performance relationship of OIHs for electrochemical water oxidation. The general principles of water oxidation will be presented first, followed by the progresses on the applications of OIHs that are classified as metal organic frameworks (MOFs) and their derivates, covalent organic framework (COF)-based hybrids and other OIHs. The roles of organic counterparts on catalytic active centers will be fully discussed and highlighted with typical examples. Finally, the challenges and perspectives assessing this promising hybrid material as an electrocatalyst will be provided. [ABSTRACT FROM AUTHOR]

An effective scheme and technical means for understanding the mechanism of interfacial charge transfer. [Display omitted] • The Z-scheme Ti-ZFO/In 2 O 3 photoelectrode was successfully constructed. • Ti-ZFO/In 2 O 3 reaches 2.2 mA/cm2 at 1.23 V vs. RHE, which is 7 times that of pure Ti-ZFO. • The Z-scheme Ti-ZFO/In 2 O 3 could promote the separation and transfer of charges effectively. • This work provides an effective method and technical means to understanding the Z-scheme mechanism. Ti-ZnFe 2 O 4 photoanode has attracted extensive attention in photoelectrochemical (PEC) water oxidation due to its narrow band gap and good photostability. However, its low efficiency limits its development. Herein, we designed and constructed direct Z-scheme Ti-ZnFe 2 O 4 /In 2 O 3 (Ti-ZFO/In 2 O 3) photoanode. Under the interface electric field, photogenerated holes with stronger oxidation capacity on In 2 O 3 are retained to participate in the water oxidation reaction, and the photocurrent density of Ti-ZFO/In 2 O 3 is much higher than that of pure Ti-ZFO, reaching 2.2 mA/cm2 at 1.23 V vs. RHE. Kelvin Probe, steady-state photovoltage spectroscopy (SPV), transient photovoltage spectroscopy (TPV) and in-situ double beam strategy were used to demonstrate the Z-scheme charge transfer mechanism of Ti-ZFO/In 2 O 3 photoanode. Our work provides an effective scheme and technical means for further understanding the mechanism of interfacial charge transfer. [ABSTRACT FROM AUTHOR]

[Display omitted] Electrochemical water splitting using hollow and defect-rich catalysts has emerged as a promising strategy for efficient hydrogen production. However, the rational design and controllable synthesis of such catalysts with intricate morphology and composition present significant challenges. Herein, we propose a template-engaged approach to fabricate a novel ball-in-ball hollow structure of Co-P-O@ N -doped carbon with abundant oxygen vacancies. The synthesis process involves the preparation of uniform cobalt-glycerate (Co-gly) polymer microspheres as precursors, followed by surface coating with ZIF-67 layer, adjustable chemical etching by phytic acid, and controllable pyrolysis at high temperature. The resulting ball-in-ball structure offers a large number of accessible active sites and high redox reaction centers, facilitating efficient charge transport, mass transfer, and gas evolution, which are beneficial for the acceleration of electrocatalytic reaction. Additionally, density functional theory (DFT) calculations indicate that the incorporation of oxygen and the presence of Co-P dangling bonds in CoP significantly enhance the adsorption of oxygenated species, leading to improved intrinsic electroactivity at the single-site level. As a sequence, the titled catalyst exhibits remarkable electrocatalytic activity and stability for water splitting in alkaline media. Notably, it only requires a low overpotential of 283 mV to achieve a current density of 10 mA cm−2 for the oxygen evolution reaction. This work may provide some new insights into the design of complex hollow structures of phosphides with abundant defects for energy conversion. [ABSTRACT FROM AUTHOR]

The efficiency of the synthesis of renewable fuels and feedstocks from electrical sources is limited, at present, by the sluggish water oxidation reaction. Single-atom catalysts (SACs) with a controllable coordination environment and exceptional atom utilization efficiency open new paradigms toward designing high-performance water oxidation catalysts. Here, using operando X-ray absorption spectroscopy measurements with calculations of spectra and electrochemical activity, we demonstrate that the origin of water oxidation activity of IrNiFe SACs is the presence of highly oxidized Ir single atom (Ir5.3+) in the NiFe oxyhydroxide under operating conditions. We show that the optimal water oxidation catalyst could be achieved by systematically increasing the oxidation state and modulating the coordination environment of the Ir active sites anchored atop the NiFe oxyhydroxide layers. Based on the proposed mechanism, we have successfully anchored Ir single-atom sites on NiFe oxyhydroxides (Ir0.1/Ni9Fe SAC) via a unique in situ cryogenic-photochemical reduction method that delivers an overpotential of 183 mV at 10 mA ⋅ cm-2 and retains its performance following 100 h of operation in 1 M KOH electrolyte, outperforming the reported catalysts and the commercial IrO2 catalysts. These findings open the avenue toward an atomic-level understanding of the oxygen evolution of catalytic centers under in operando conditions.

Abstract How to put together a comprehensive water oxidation design is the long‐term problem for the generation of sustainable fuels. In nature, plants are equipped with a complex mechanism (the Calvin cycle) in the stroma that, over the billions of years, efficiently takes CO2 and converts it to sugar. This reductive process needs electrons from an oxygen‐evolving complex (OEC) in the core of photosystem II, where a water oxidation reaction (WOR) releases molecular oxygen. The initial function of proton relays in natural WOR happens when Tyrosine Yz is oxidized by light harvested P680 through a proton‐coupled electron transfer reaction. The second and main one, is composed of water‐included polypeptide channels from and to CaMn4O5. These channels were created utilizing hydrogen‐bonded networks (HBN). HBN is crucial in providing water substrate and removing the released protons to prevent the accumulation of protons and preserve the stability of the catalytic center. This concept summarizes the challenges in employing biomimicry to create artificial leaves from the viewpoint of proton relays, with the main purpose being providing structural functionality to assist the quick proton hopping.

Water oxidation (WO) is the first step in the water-splitting process aiming at the production of hydrogen as a green renewable fuel. To successfully perform WO, potent strategies for overcoming the high energetic barrier and slow kinetics of this reaction are urgently required. One such strategy is the use of molecular catalysis. Specifically, Cu-based catalysts have been highlighted over the last decade due to their stability and fast kinetics. Among them, Cu-peptoids, where peptoids are peptidomimetics akin to peptides and are N-substituted glycine oligomers, can act as stable and active catalysts for oxidation transformations including electrocatalytic WO. Previously, we suggested that a benzyl group incorporated as a side chain near the catalytic site within a Cu-peptoid electrocatalyst for WO has a structural role in the activity of the electrocatalyst in phosphate buffer (PBS). Herein, we aimed to test this hypothesis and understand how an incorporated structural element side chain affects WO. To this aim, we prepared a set of peptoid trimers each with a different structural element replacing the benzyl group by either naphthyl, cyclohexyl, benzyl, propyl chloride, or propyl side chains as well as a peptoid lacking a structural element. We studied the structure of their Cu complexes and tested these complexes as electrocatalysts for WO. We discovered that while all the peptoids self-assemble to form dinuclear Cu-peptoid complexes, the duplex that has no structural side chain, Cu2(BE)2, is structurally different from the others in the solid state. Moreover, Cu2(BE)2 remains dinuclear in a PBS at pH 11, while all the other duplexes are mononuclear in the PBS. Finally, though most of the complexes showed low electrocatalytic activity for WO, the dinuclear complex Cu2(BE)2 performed with the highest turnover frequency of 484 s−1. Nevertheless, this dinuclear complex slowly decomposes to the corresponding mononuclear complex as a more stable species during WO, while the other mononuclear complexes retain their structure in solution but display much slower kinetics (ca. 5 to 8 s−1) under the same conditions. Overall, our results demonstrate that bulkier side chains hamper the stability of dinuclear Cu-peptoids in a PBS, and hence, their efficiency as WO electrocatalysts is also hampered. [ABSTRACT FROM AUTHOR]

In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the room-temperature structures of PS II in the four (semi)stable S-states, S1, S2, S3, and S0, showing that a water molecule is inserted during the S2 → S3 transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O2 formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S2 → S3 transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QA and QB, are observed. At the donor site, tyrosine YZ and His190 H-bonded to it move by 50 µs after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of OX(H) at the open coordination site of Mn1. This water, possibly a ligand of Ca, could be supplied via a "water wheel"-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (τ of ∼350 µs) during the S2 → S3 transition mirrors the appearance of OX electron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.

Abstract As the most desirable hydrogen production device, the highly efficient acidic proton exchange membrane water electrolyzers (PEMWE) are severely limited by the sluggish kinetics of oxygen evolution reaction (OER) at the anode. Rutile IrO2 is a commercial acid‐stable OER catalyst with poor activity and high cost, which has motivated the development of alternatives. However, hitherto most of the designed acidic OER catalysts have disadvantages of low activity or stability, which cannot meet the requirement of industrial applications. Thus, exploring suitable strategies to enhance the activity and stability of cost‐effective acidic OER catalysts is crucial for developing the PEMWE technique. In this review, the main OER mechanisms, different types of catalysts, and their activity and stability characteristics are summarized and discussed, and then possible strategies to improve activity and stability are proposed. Finally, the problems and prospects of such catalysts are generalized to shed some light on the future research of advanced catalysts for acidic OER.

Abstract A rational regulation of the solar water splitting reaction pathway by adjusting the surface composition and phase structure of catalysts is a substantial approach to ameliorate the sluggish reaction kinetics and improve the energy conversion efficiency. In this study, we demonstrate a nanocrystalline iron pyrophosphate (Fe4(P2O7)3, FePy)-regulated hybrid overlayer with amorphous iron phosphate (FePO4, FePi) on the surface of metal oxide nanostructure with boosted photoelectrochemical (PEC) water oxidation. By manipulating the facile electrochemical surface treatment followed by the phosphating process, nanocrystalline FePy is localized in the FePi amorphous overlayer to form a heterogeneous hybrid structure. The FePy-regulated hybrid overlayer (FePy@FePi) results in significantly enhanced PEC performance with long-term durability. Compared with the homogeneous FePi amorphous overlayer, FePy@FePi can improve the charge transfer efficiency more significantly, from 60% of FePi to 79% of FePy@FePi. Our density-functional theory calculations reveal that the coexistence of FePi and FePy phases on the surface of metal oxide results in much better oxygen evolution reaction kinetics, where the FePi was found to have a typical down-hill reaction for the conversion from OH* to O2, while FePy has a low free energy for the formation of OH*. Graphical abstract

Molecular copper water oxidation electrocatalysts have been extensively studied in recent years for their potential use in artificial photosynthetic systems for solar energy conversion. Although ligand modification and its ability to influence catalytic properties is a key advantage of molecular systems, there are, as yet, few examples of systematic studies of these effects. Our oxidatively resistant pyalk (2-pyridyl-2-propanoate) ligand forms a complex with copper(II) that catalyzes water oxidation and provides an attractive scaffold for systematic ligand tuning. Here, we report a series of analogous copper complexes with electron-donating (methoxy-) and -withdrawing (methoxycarbonyl-) groups at the para-position of the pyalk ligand. Trends in the pKa and redox potential align with first-principles predictions for the electron-withdrawing and electron-donating groups. While the modified complexes show good activity for water oxidation, lowered faradaic efficiency in comparison to the parent complex highlights the importance of stability considerations for catalyst tuning. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting in a pH-neutral electrolyte has attracted more and more attention in the field of sustainable energy. Bismuth vanadate (BiVO4) is a highly promising photoanode material for PEC water splitting. Additionally, cobaltous phosphate (CoPi) is a material that can be synthesized from Earth's rich materials and operates stably in pH-neutral conditions. Herein, we propose a strategy to enhance the charge transport ability and improve PEC performance by electrodepositing the in situ synthesis of a CoPi layer on the BiVO4. With the CoPi co-catalyst, the water oxidation reaction can be accelerated and charge recombination centers are effectively passivated on BiVO4. The BiVO4/CoPi photoanode shows a significantly enhanced photocurrent density (Jph) and applied bias photon-to-current efficiency (ABPE), which are 1.8 and 3.2 times higher than those of a single BiVO4 layer, respectively. Finally, the FTO/BiVO4/CoPi photoanode displays a photocurrent density of 1.39 mA cm−2 at 1.23 VRHE, an onset potential (Von) of 0.30 VRHE, and an ABPE of 0.45%, paving a potential path for future hydrogen evolution by solar-driven water splitting. [ABSTRACT FROM AUTHOR]

The development of stable and efficient electrocatalysts for oxygen evolution reaction is of great significance for electro-catalytic water splitting. Bimetallic layered double hydroxides (LDHs) are promising OER catalysts, in which NiCu LDH has excellent stability compared with the most robust NiFe LDH, but the OER activity is not satisfactory. Here, we designed a NiCu LDH heterostructure electrocatalyst (Cu/NiCu LDH) modified by Cu nanoparticles which has excellent activity and stability. The Cu/NiCu LDH electrocatalyst only needs a low over-potential of 206 mV and a low Tafel slope of 86.9 mV dec−1 at a current density of 10 mA cm−2 and maintains for 70 h at a high current density of 100 mA cm–2 in 1M KOH. X-ray photoelectron spectroscopy (XPS) showed that there was a strong electronic interaction between Cu nanoparticles and NiCu LDH. Density functional theory (DFT) calculations show that the electronic coupling between Cu nanoparticles and NiCu LDH can effectively improve the intrinsic OER activity by optimizing the conductivity and the adsorption energy of oxygen-containing intermediates. [ABSTRACT FROM AUTHOR]

The collection of solar energy in chemical bonds via dye-sensitized photoelectrosynthesis cells (DSPECs) is a reliable solution. Herein, atomic layer deposition (ALD) introduced ultrathin blocking layers (BLs) between a mesoporous TiO2 membrane and fluorine-doped tin oxide (FTO), and much improved photoelectrochemical water oxidation performance was well documented. Samples with different BL thicknesses deposited on FTO were obtained by ALD. In the photoanode, polypyridyl Ru(II) complexes were used as photosensitizers, and Ru(bda)-type was used as a catalyst during water oxidation. Under one sun irradiation, the BL (i) increased the photocurrent density; (ii) slowed down the open-circuit voltage decay (OCVD) by electrochemical measurement; (iii) increased the photo-generated electron lifetime roughly from 1 s to more than 100 s; and (iv) enhanced the water oxidation efficiency from 25% to 85% with 0.4 V of applied voltage bias. All this pointed out that the ALD technique-prepared layers could greatly hinder the photogenerated electron–hole pair recombination in the TiO2-based photoanode. This study offers critical backing for the building of molecular films by the ALD technique to split water effectively. [ABSTRACT FROM AUTHOR]

Anionic High-entropy materials have seldom been reported as a new library of water oxidation electrocatalysts owing to great difficulty in uniformly distributing multiple elements with different physicochemical properties and harsh synthesis conditions. Herein, a series of amorphous quasi-high-entropy carbonates for the first time is prepared via a facile low-temperature hydrothermal route. The optimized CoCrFeMnMoCO 3 with hydrothermal treatment of 6 h can serve as a promising oxygen evolution reaction (OER) electrocatalyst for water splitting on account of amorphous structure rendering more exposed active sites, superior synergistic effect realizing surface component self-optimization, high-valence ferritic species (Fe(3+δ)+) providing high catalytic activity and high-entropy stabilization guaranteeing long-term OER performance, thus exhibiting the low overpotentials of 302 and 355 mV at the current densities of 10 and 100 mA cm−2, respectively, the small Tafel slope of 36.7 mV dec−1, and excellent durability longer than 38 h, dramatically exceeding its corresponding crystalline counterpart and benchmark RuO 2 catalyst, as well as yielding the current density of 10 mA cm−2 with impressive low voltage of 1.56 V while used as bifunctional electrocatalyst for overall water splitting. This study lights a broad avenue to design other anionic high-entropy materials as promising OER catalysts. [ABSTRACT FROM AUTHOR]

Modern‐day society requires advanced technologies based on renewable and sustainable energy resources to face the challenges regarding environmental remediation. Solar‐inspired photocatalytic applications for water purification, hydrogen and oxygen evolution, carbon dioxide reduction, nitrogen fixation, and removal of bacterial species seem to be unique solutions based on green and efficient technologies. Considering the unique electronic features and larger surface area, 2D photocatalysts have been broadly explored for the above‐mentioned applications in the past few years. However, their photocatalytic potential has not been optimized yet to the adequate level of practical and commercial applications. Among many strategies available, surface and interface engineering and the hybridization of different materials have revealed pronounced potential to boost the photocatalytic potential of 2D materials. This feature review recapitulates recent advancements in engineered materials that are 2D for various photocatalysis applications for environmental remediation. Various surface and interface engineering technologies are briefly discussed, like anion–cation vacancies, pits, distortions, associated vacancies, etc., along with rules and parameters. In addition, several hybridization approaches, like 0D/2D, 1D/2D, 2D/2D, and 3D/2D hybridization, etc., are also deeply investigated. Lastly, the application of these engineered 2D materials for various photocatalytic applications, challenges, and future perspectives is extensively explored. [ABSTRACT FROM AUTHOR]

A highly efficient visible-light-driven photoanode, N2-intercalated tungsten trioxide (WO3) nanorod, has been controllably synthesized by using the dual role of hydrazine (N2H4), which functioned simultaneously as a structure directing agent and as a nitrogen source for N2 intercalation. The SEM results indicated that the controllable formation of WO3 nanorod by changing the amount of N2H4. The β values of lattice parameters of the monoclinic phase and the lattice volume changed significantly with the nW: nN2H4 ratio. This is consistent with the addition of N2H4 dependence of the N content, clarifying the intercalation of N2 in the WO3 lattice. The UV-visible diffuse reflectance spectra (DRS) of N2-intercalated exhibited a significant redshift in the absorption edge with new shoulders appearing at 470–600 nm, which became more intense as the nW:nN2H4 ratio increased from 1:1.2 and then decreased up to 1:5 through the maximum at 1:2.5. This addition of N2H4 dependence is consistent with the case of the N contents. This suggests that N2 intercalating into the WO3 lattice is responsible for the considerable red shift in the absorption edge, with a new shoulder appearing at 470−600 nm owing to formation of an intra-bandgap above the VB edges and a dopant energy level below the CB of WO3. The N2 intercalated WO3 photoanode generated a photoanodic current under visible light irradiation below 530 nm due to the photoelectrochemical (PEC) water oxidation, compared with pure WO3 doing so below 470 nm. The high incident photon-to-current conversion efficiency (IPCE) of the WO3-2.5 photoanode is due to efficient electron transport through the WO3 nanorod film. [ABSTRACT FROM AUTHOR]

Mn-oxidizing microorganisms oxidize environmental Mn(II), producing Mn(IV) oxides. Pseudomonas putida MnB1 is a widely studied organism for the oxidation of manganese(II) to manganese(IV) by a multi-copper oxidase. The biogenic manganese oxides (BMOs) produced by MnB1 and similar organisms have unique properties compared to non-biological manganese oxides. Along with an amorphous, poorly crystalline structure, previous studies have indicated that BMOs have high surface areas and high reactivities. It is also known that abiotic Mn oxides promote oxidation of organics and have been studied for their water oxidation catalytic function. MnB1 was grown and maintained and subsequently transferred to culturing media containing manganese(II) salts to observe the oxidation of manganese(II) to manganese(IV). The structures and compositions of these manganese(IV) oxides were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma optical emission spectroscopy, and powder X-ray diffraction, and their properties were assessed regarding catalytic functionality towards water oxidation in comparison to abiotic acid birnessite. Water oxidation was accomplished through the whole-cell catalysis of MnB1, the results for which compare favorably to the water-oxidizing ability of abiotic Mn(IV) oxides.

Mimicking the photosynthesis of green plants to combine water oxidation with CO2 reduction is of great significance for solving energy and environmental crises. In this context, a trinuclear nickel complex, [NiII3(paoH)6(PhPO3)2]·2ClO4 (1), with a novel structure has been constructed with PhPO32− (phenylphosphonate) and paoH (2-pyridine formaldehyde oxime) ligands and possesses a reflection symmetry with a mirror plane revealed by single-crystal X-ray diffraction. Bulk electrocatalysis demonstrates that complex 1 can homogeneously catalyze water oxidation and CO2 reduction simultaneously. It can catalyze water oxidation at a near-neutral condition of pH = 7.45 with a high TOF of 12.2 s−1, and the Faraday efficiency is as high as 95%. Meanwhile, it also exhibits high electrocatalytic activity for CO2 reduction towards CO with a TOF of 7.84 s−1 in DMF solution. The excellent electrocatalytic performance of the water oxidation and CO2 reduction of complex 1 could be attributed to the two unique µ3-PhPO32− bridges as the crucial factor for stabilizing the trinuclear molecule as well as the proton transformation during the catalytic process, while the oxime groups modulate the electronic structure of the metal centers via π back-bonding. Therefore, apart from the cooperation effect of the three Ni centers for catalysis, simultaneously, the two kinds of ligands in complex 1 can also synergistically coordinate the central metal, thereby significantly promoting its catalytic performance. Complex 1 represents the first nickel molecular electrocatalyst for both water oxidation and CO2 reduction. The findings in this work open an avenue for designing efficient molecular electrocatalysts with peculiar ligands.

In the present work, nickel-iron layered double hydroxide was prepared by the hydrothermal method. The synthesized electrocatalyst was studied using X-ray diffraction pattern, infrared spectroscopy, nitrogen absorb-desorption, and scanning electron microscopy. The results confirmed the synthesis of a high surface area electrocatalyst. In the next step, the electrocatalytic activity of the synthesized sample was investigated by dropping the sample on the glassy carbon electrode at neutral media. The voltammetric results show a decrease in the onset potential and overpotential of hydrothermal nickel-iron layered double hydroxide in compared to the nickel-iron layered double hydroxide which was synthesized by the co-precipitation method. High surface area, low onset potential, high stability, and repeatability are the prominent features of this electrocatalyst.

[Display omitted] • Cobalt phosphides have been developed as co-catalyst to boost BiVO 4 photoanode for H 2 O 2 production. • Co site is presented to promote the breaking of one H O bond in water to form OH•. • P site plays an important role in the desorption of the formed H 2 O 2. Photoanodic hydrogen peroxide (H 2 O 2) production via water oxidation is limited by low yields and poor selectivity. Herein, four variations of cobalt phosphides, including pristine CoP and Co 2 P crystals, and two mixed-phase cobalt phosphides (CoP/Co 2 P) with different ratios, were applied as co-catalysts on the BiVO 4 (BVO) photoanode to improve H 2 O 2 production. The optimal yield and selectivity were approximately 9.6 µmol‧h−1‧cm−2 and 25.2 % at a voltage bias of 1.7 V vs reversible hydrogen electrode (V RHE) under sunlight illumination, respectively. This performance is approximately 1.8 times that of pristine BVO photoanode. The roles of the Co and P sites were investigated. In particular, the Co site promotes the breaking of one H O bond in water to form OH• radicals, which is the rate-determining step in H 2 O 2 production. The P site plays an important role in the desorption of H 2 O 2 formed from the catalyst, which is responsible for the recovery of fresh catalytic sites. Among the four samples, Co 2 P exhibited the best performance for H 2 O 2 production because it had the highest rate of OH• formation owing to its improved accumulation property. This study offers a rational design strategy for co-catalysts for photoanodic H 2 O 2 production. [ABSTRACT FROM AUTHOR]

Due to energy crises and environmental pollution worldwide, researchers have sought efficient electrocatalysts for oxygen evolution reaction (OER) and photocatalysts to eliminate organic pollutants. In the present work, we have synthesized a fullerene-C 60 -based CeO 2 @C 60 core-shell hybrid and characterized it with various state-of-art techniques to explore its OER performance and photocatalytic properties under natural sunlight. TEM nano-graphs and EDX color mapping exhibited the uniform covering of C 60 over CeO 2 forming a core-shell structure with a particle size of 54 nm. The XPS results demonstrate the coexistence of Ce3+ and Ce4+ oxidation states, resulting in the formation of rich oxygen vacancy defects, which induced the efficient charge transformation from CeO 2 to C 60 , enhancing the photocatalytic activity and promoting the OER reaction. The electrochemical measurements revealed a lower overpotential (312 mV) and small Tafel slope (54 mV/dec) at 10 mA/cm2 current density of CeO 2 @C 60 core-shell hybrid than pure CeO 2. Further, the hybrid is stable up to 2000th cycles, and the chronoamperometry test showed that it remains stable for 45 hr without degrading in 1 M KOH solution. The photocatalytic activity under natural sunlight irradiations showed that the CeO 2 @C 60 core-shell hybrid completely degraded P-nitroaniline (P-Nitro) organic pollutant after 75 min, with outstanding recyclability up to the 7th cycle of use. Furthermore, the present work explores the tremendous potential of C 60 and rare earth metal oxide-based hybrid catalysts having exceptional stability toward photocatalysis and electrochemical water splitting. [Display omitted] [ABSTRACT FROM AUTHOR]

One mononuclear Mn(III) complex [MnIIIL(H2O)(MeCN)](ClO4) (1) and one hetero-binuclear complex [(CuIILMnII(H2O)3)(CuIIL)2](ClO4)2·CH3OH (2) have been synthesized with the Schiff base ligand (H2L = N,N′-bis(3-methoxysalicylidene)-1,2-phenylenediamine). Single crystal X-ray structural analysis manifests that the Mn(III) ion in 1 has an octahedral coordination structure, whereas the Mn(II) ion in 2 possesses a trigonal bipyramidal configuration and the Cu(II) ion in 2 is four-coordinated with a square-planar geometry. Electrochimerical catalytic investigation demonstrates that the two complexes can electrochemically catalyze water oxidation and CO2 reduction simultaneously. The coordination environments of the Mn(III), Mn(II), and Cu(II) ions in 1 and 2 were provided by the Schiff base ligand (L) and labile solvent molecules. The coordinately unsaturated environment of the Cu(II) center in 2 can perfectly facilitate the catalytic performance of 2. Complexes 1 and 2 display that the over potentials for water oxidation are 728 mV and 216 mV, faradaic efficiencies (FEs) are 88% and 92%, respectively, as well as the turnover frequency (TOF) values for the catalytic reduction of CO2 to CO are 0.38 s−1 at −1.65 V and 15.97 s−1 at −1.60 V, respectively. Complex 2 shows much better catalytic performance for both water oxidation and CO2 reduction than that of complex 1, which could be owing to a structural reason which is attributed to the synergistic catalytic action of the neighboring Mn(III) and Cu(II) active sites in 2. Complexes 1 and 2 are the first two compounds coordinated with Schiff base ligand for both water oxidation and CO2 reduction. The finding in this work can offer significant inspiration for the future development of electrocatalysis in this area. [ABSTRACT FROM AUTHOR]

Activation of narrow bandgap photocatalysts is a prerequisite for the efficient production of renewable hydrogen from water using sunlight. Loading of dual cocatalysts intended to promote reduction and oxidation reactions by photodeposition is known to greatly enhance the water splitting activity of certain oxide photocatalysts. However, it is difficult to photodeposit oxygen evolution cocatalysts onto narrow bandgap oxynitride photocatalysts because the driving forces for the necessary oxidation reactions are weak. The present work demonstrates oxidative photodeposition of the Fe-based cocatalyst FeOx onto a Mg-doped BaTaO2N photocatalyst having an absorption edge wavelength of 620 nm. This modification enhances the oxygen evolution activity of the photocatalyst more effectively than conventional impregnation methods. The rapid removal of photoexcited electrons from the photocatalyst by a reduction cocatalyst (Pt) and an electron acceptor (molecular oxygen) are evidently necessary for the photodeposition of the FeOx cocatalyst. A Mg-doped BaTaO2N photocatalyst coloaded with Pt and FeOx exhibits an apparent quantum yield of 1.2% at 420 nm during the oxygen evolution reaction in an aqueous AgNO3 solution. This photodeposition procedure does not involve any heat treatment and so provides new opportunities for the design and construction of oxygen evolution sites on narrow-bandgap non-oxide photocatalysts that may be prone to thermal decomposition. [ABSTRACT FROM AUTHOR]

The understanding of light‐induced biological water oxidation in oxygenic photosynthesis is of great importance both for biology and (bio)technological applications. The chemically difficult multistep reaction takes place at a unique protein‐bound tetra‐manganese/calcium cluster in photosystem II whose structure has been elucidated by X‐ray crystallography (Umena et al. Nature 2011, 473, 55). The cluster moves through several intermediate states in the catalytic cycle. A detailed understanding of these intermediates requires information about the spatial and electronic structure of the Mn4Ca complex; the latter is only available from spectroscopic techniques. Here, the important role of Electron Paramagnetic Resonance (EPR) and related double resonance techniques (ENDOR, EDNMR), complemented by quantum chemical calculations, is described. This has led to the elucidation of the cluster's redox and protonation states, the valence and spin states of the manganese ions and the interactions between them, and contributed substantially to the understanding of the role of the protein surrounding, as well as the binding and processing of the substrate water molecules, the O‐O bond formation and dioxygen release. Based on these data, models for the water oxidation cycle are developed. [ABSTRACT FROM AUTHOR]

Fossil fuels are facing various challenges, such as global warming and depletion of fossil energy sources. Fortunately, hydrogen energy can be a green energy source for sustainable development. Hydrogen production from electrolytic water is one of the most efficient methods in the hydrogen energy industry; however, the realization of an efficient electrochemical oxygen evolution reaction (OER) is the key to hydrogen production from electrolytic water. As a result, developing noble metal-free electrocatalysts with high activity and alkaline stability is critical. This article gives a focused evaluation of the most recent highly active oxygen evolution catalysts in this new research field. The mechanism of the OER catalyst in an alkaline environment is discussed first, followed by the fundamental needs of catalysts for the oxygen evolution process. Then, contemporary researchers' design alternatives for enhancing OER active materials are explored, as well as new developments and discoveries of current advanced noble metal-free active materials. Finally, the problems and future prospects for developing efficient catalyst systems for industrial applications are discussed. Future research directions are also pointed out for the preparation of resource-rich emerging nonprecious metal OER electrocatalysts in alkaline environments. [ABSTRACT FROM AUTHOR]

Ni(OAc) 2.4H 2 O and CoCl 2.6H 2 O reacted with thiazole ligands, HL and HL' (where HL= (E)-2-(((4-phenylthiazol-2-yl)imino)methyl)phenol and HL'= (Z)-2-(2-benzylidenehydrazinyl)-4-phenylthiazole, in ethanol to create new mononuclear Co(II) and Ni(II) complexes, CoL 2 , NiL 2 , CoL' 2 , and NiL' 2 (1 - 4). X-ray diffraction analysis, spectroscopic, and electrochemical methods were used to study the complexes. A carbon paste electrode that had been modified by complexes 1 - 4 was used as the working electrode in a three-electrode setup to test the complexes' ability in water oxidation reaction at pH 13. The linear sweep voltammetry (LSV) curves showed that complexes 3 and 2 have much greater activity and only require the overpotential of 570 and 690 mV ʋs. RHE at a current density of 10 mA/cm2 with Tafel slopes of 86.92 and 94.19 mVdec−1 respectively in an alkaline solution. In addition, the amperometry tests exhibited brilliant stability for water oxidation by CPE-complex 3 and CPE-complex 2 under electrochemical conditions at pH 13. Although X-ray diffraction patterns did not display a crystalline structure, the scanning electron microscopy images displayed that cobalt oxide and nickel oxide in an alkaline condition are proper catalysts for water oxidation reaction on the surface of the modified electrode. • We synthesized new thiazole Schiff base complexes of Co(II) and Ni(II). • These complexes can catalyze the oxidation of water in alkaline solution electrochemicaly. • Two of the complexes showed significantly higher activity by lowering Tafel slopes and overpotentials. • The surfaces of working electrodes modified by complexes are confirmed to have amorphous cobalt and nickel oxides by EDX and XRD analysis. [ABSTRACT FROM AUTHOR]